16. http://www.youtube.com/watch?v=b6MVPYG veeQ&feature=related

17. http://www.youtube.com/watch?v=P96XG4Pa4OY

19. In this figure, you can see that a relay consists of two separate and completely independent circuits. The first is at the bottom and drives the electromagnet. In this circuit, a switch is controlling power to the electromagnet. electromagnet When the switch is on, the electromagnet is on, and it attracts the armature (blue). The armature is acting as a switch in the second circuit. When the electromagnet is energized, the armature completes the second circuit and the light is on. When the electromagnet is not energized, the spring pulls the armature away and the circuit is not complete. In that case, the light is dark.

23. Clip http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/m agnetostatics/14-SeriesWires/14-Series_320.html

24. CLIP http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/magnetostatic s/16-MagneticForceRepel/16-MagForceRepel_f65_320.html

25. Clip http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/magne tostatics/13-ParallelWires/13-Parallel_Wires_320_f185.html

26. CLIP http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/magneto statics/15-MagneticForceAttract/15-MagForceAtt_f65_320.html